Method of treating a petroleum producing formation



G. HERZOG Sept. 29, 1959 METHOD OF TREATING A PETROLEUM PRODUCING FORMATION vFiled April 5, 1956 Tlzll.

M//M/g United States Patent Oce Patented Sept. 29, 19,512

METHOD F TREATIN G A PETROLEUM PRODUCING FORMATION Gerhard Herzog, Houston, Tex., assigner to Texac'o Inc., a corporation of Delaware Application April 5, 1956, Serial No. '576,486

7 Claims. (Cl. 16639) This invention relates to the production of petroleum from underground petroleum producing form-ations. More particularly, this invention relates to the treatment of underground petroleum producingformations.

Various techniques have been proposed for the recovery of petroleum from underground formations and for the treatment of petroleum producing formations. For the recovery of petroleum from petroleum producing formations secondary recovery operations which involve water ooding o-r thermal recovery methods, in situ combustion, involving at least one injection well and at least one production well have been proposed. Further, it has also been proposed to increase the productivity of a given well by blasting, acidizing or hydraulically fracturing the petroleum producing formation traversed by the well bore. Various other methods have also been proposed to improve the oil permeability of underground petroleum producing formations. In general, however, all these proposed methods have not always yielded the sought for results.

Many petroleum producing formations are not satisfactorily treated by acidizin-g or by hydraulic fracturing. Blasting an underground producing formation to increase its porosity and/ or permeability in the vicinity of the well bore is a relatively dangerous operation. Secondary recovery methods employing water flooding or thermal recovery methods employing in situ combustion in combination with an injection well and a production well involve at least two or more wells as well as the expenditure of co-nsiderable capital, equipment, material and time before appreciable tangible results are observable.

In accordance with the practice o-f this invention that portion of a petroleum producing formation inv the vicinity of or surrounding a well bore is treated to effect in situ combustion of a combustible material therein. Subsequently petroleum is produced via the -Well bore through that portion of the petroleum producing formation wherein in situ combustion was effected.

Explanatory of in situ combustion as employed in the practice of this invention, a high temperature zone is established in the petroleum producing formation `in vthe vicinity of the well bore by suitable heating means. -Suitable heating means may comprise an electrical heating device or a `gas red bottom hole igniter or heater;r` A suitable device for initiating in situ combustion withina bore hole is described in U.S. 2,722,278. Upon introducing a combustion-supporting or an oxygen-containing gas such as air into the petroleum producing formation vi-a the well bore a high temperature combustion orireaction zone created by the reaction between ythe oxygen and combustible residues within the formation, such-as combustible residues resulting from the distillation and/ or thermal cracking of crude oil originally in place or introduced therein, will commence to move into the formation outwardly from the well bore.

Leaving this high temperature zone is a relatively high temperature gas stream which, as it moves outwardly into the formation, losses heat to the formation. By this method the high temperature reaction zone is moved for a considerable distance, for example a distance in the range 3'-25 feet, more or less, radially outwardly from the well bore without further direct application of heat to the area immediately surrounding the Accordingly, it is an object of this invention to prol vide an improved method for the treatment of underground petroleum producing formations to enhance or otherwise improve -the recovery of petroleum therefrom.

It is another object of this invention to provide a generally applicable method for the treatment ofv underground petroleum producing formations.

I t is still another object of this invention to provide a method for increasing the oil permeability of anundergroundproducing formation in that portion of the producing formation surrounding a well bore.

f Still another object of this invention is vto provide a method for dissipating or removing a lwater block and for otherwise improving the petroleuminormally gaseous and/or normally liquid hydrocarbons) permeability of that portion of thepetroleum producing formation surrounding a well bore through which petroleum is produced.- Y

How these and other objects of this invention are achieved will become apparent inthe light of the accompanying disclosure and drawings wherein Fig. 1 schematically illustrates a method in accordance with the practice of this invention as applied to an underground petroleum producing formation and Fig. 2 is anexplana-` well bore. Continued direct application of heat to the area immediately surrounding the well bore may be desirable however. The distance the high temperature reaction zone moves radially outwardly and as a result the volume of the petroleum producing formation swept by or comprised within the in situ combustion zone is determined by the relative magnitude of the rate of heat generation (combustion of combustible residues) and the rate of heat loss to the surrounding formations.

It has been postulated that the following mechanisms are important in the movement of the high temperature reaction zone radially outwardly from a well bore into the petroleum producing formation during in situ cornbustion. Although 4the exact mechanism of in situr'combustion is not definitely known, the following sequence of events in an underground in situ combustion operation are postulated and are presented hereinv for the purpose of enabling one skilled in the art'to better lunder'- stand this invention and are not to be construed as limiting this invention in any way.

As the high temperature reaction zone approaches any.` given volume of the petroleum producing formation the temperature of this volume of formation rises. This results in first a reduction in the viscosity ofthe formation liquids due to their temperature increase. These liquids may then be moved more readily under the influence of the gas stream continuously emanating from the high temperature reaction zone. As the temperature continues to rise, distillations of the formation liquids begins. The

. products of these distillations condense in cooler regions of the formation removed from the high temperature reaction zone. The distillations continue as 'the 'tern-l perature continues to rise until the heavier componentsv remaining from the crude toil originally in place within the formation or introduced thereinto prior 'to effecting in situ'combustion begin to crack yielding hydrocarbon gases, hydrogen and :the like'and coke-'or similar solid'l carbonaceous residues. As the tempearture continues to rise and the oxygen content of the incoming gas vincreases due to depletion ofrvcombustibleresidues ,in preceding.

regions of the formation, a point will be reached at which the coke or other combustible residue will begin to react with oxygen with the resulting release of heat to the formation and the gas stream. This heat is carried away by the on-moving gas stream and also to some extent by conduction to adjoining regions of the formation. When the coke or combustible residue has been burned away there remains a volume of liquid-free formation which, unless otherwise treated, is gradually cooled by the relatively cool combustion supporting gas entering the formation via the well bore.

From the above considerations it is obvious that the rate of heat energy released within the formation should be some function of the quantity of the fuel present therein, which is dependent upon the type and quantity of crude originally in place and/ or combustible material or fuel caused to be deposited therein, and that the rate of release should also be dependent upon the rate at which oxygen is supplied to the combustion zone. The rate at which heat can be transferred ahead of the high temperature reaction or combustion zone should be dependent on the rate at which combustion gas leaves the reaction zone and should be to some extent dependent upon conduction through the formation itself. Accordingly, some control of the in situ combustion process can be exercised by controlling the composition, such as oxygen content, of the injected combustion supporting oxygencontaining gas.

The physical characteristics and properties of the formation swept by the high temperature reaction or combustion zone and other portions of the formation otherwise influenced by the high temperature gas stream emanating from the reaction zone will probably be favorably altered with respect to oil permeability. That portion of the petroleum producing formation swept by the high temperature combustion zone will exhibit improved porosity and/or permeability values with respect to the production of petroleum therethrough. It is believed that the high temperature developed within the reaction zone will cause clays subjected thereto to lose water and otherwise become dehydrated with resulting volume shrinkage. It is also believed that some thermal fracturing of the formation swept or otherwise influenced by the high temperature reaction zone will also be accomplished, e.g., by sheer expansion of the formation along formation discontinuities and the like, leading to fractures and fissures and increasing the porosity of the formation in the portion swept by in situ combustion. Further, it is believed that the high temperatures generated at the high temperature reaction zone in the range 70D-2500a F., usually in the range 800-1500 F., will eventually effect calcination or thermal decomposition of many of the minerals, such as limestone or dolomite, present within the formation exposed to these high temperatures, with the resultant production of gaseous or water-soluble decomposition products. Accordingly, when the formation is again produced through that portion swept by the high temperature reaction zone the resulting gaseous and/or water-soluble decomposition products, such as CO2 or CaO, are swept out, dissolved and otherwise removed by the return 'of liquid water accompanying the produced petroleum.

Referring now to the drawing which schematically illustrates one embodiment of the practice of this invention, there is illustrated a well bore 11 penetrating substantially impermeable formations 12 and 14 which, respectively, adjoin the upper and lower boundaries of petroleum producing formation 15. A casing 16 is positoned Within well bore 11 and is provided with perforations 17 adjacent the petroleum producing formation 15. A packer 13 is provided in the lower part of casing 16 such as at aboutA the lower portion of petroleum Vproducing formation 15.

As previously indicated, the practice of this invention is particularly applicable to the treatment of petroleum producing formations which evidence a substantially reduced oil permeability in the vicinity of the well bore through which the formation is produced. The reduced oil permeability of the formation in a zone surrounding the well bore may be caused by the deposition of detritus or solid hydrocarbonaceous material (paraffin) within the interstices of the formation surrounding the well bore. Particularly adaptable for treatment in accordance with the practice of this invention is a petroleum producing formation which evidences or has experienced a water block in the vicinity of the producing well bore. This water block or zone of reduced oil permeability may have been brought about, after the well has `been shut in, by the dumping of a water column back into the producing formation. In which event a producing formation in the zone immediately adjacent or surrounding the well bore will contain a substantial amount of water or will be substantially saturated therewith, and will evidence a low oil permeability.

In accordance with one practice of this invention, especially if the amount of petroleum originally in place in the zone immediately surrounding the well bore within the petroleum producing formation, is insuicient to support in situ combustion therein, there is introduced into the formation via production casing 16 and perforations 17 an amount of a combustible fluid, preferably a liquid, such as a crude oil or fraction thereof, which when subjected to a relatively elevated temperature or upon thermal cracking tends to deposit a solid combustible carbonaceous residue, such as asphalt or coke and the like. The amount of liquid thus introduced into the petroleum producing formation usually is equivalent to at least about the pore volume of that portion of the petroleum producing formation undergoing treatment extending for a distance in the range l-Sfeet, more or less, radially outwardly from well bore 11. The limit of that zone of the petroleum producing formation surrounding the well bore and into which the combustible liquid is injected or otherwise occupied by a combustible liquid such as crude oil originally in place or injected thereinto is indicated by dashed line 18.

After a suitable amount of combustible liquid is present within zone 18 of petroleum producing formation 16 the liquid is ignited in situ in the region immediately adjacent the well bore 11 by suitable means, such as by radiant heating and/or by the injection of a high temperature oxygen-containing stream of air or by means of hot combustion gases introduced via casing 16 and perforations 17.

After in situ combustion in the area of the producing formation immediately adjacent Well bore 11 has been initiated there is introduced via casing 16 and the perforations 17 a combustion supporting stream such as an oxygen-containing stream, oxygen content in the range 1.5-20%, for example in the range 3-10% by vol., more or less, to effect continued in situ combustion of the injected combustible liquid and/or petroleum originally in place within the producing formation. The introduction of the oxygen-containing stream is continued until the in situ combustion Within the petroleum producing formation has been carried out to the desired extent. The forward limit of the in situ combustion zone or high temperature combustion zone is indicated by dashed line 19. Generally, effective results will be obtained by carrying out in situ combustion within the petroleum producing formation within that volume of the formation encompassed by about 5-50, more or less, radial feet from well bore 11.

After a sufficient volume of producing formation 15 has been swept by in situ combustion the supply of oxygencontaining gas is stopped and production from the thustreated producing formation can be resumed. At first, it is postulated, as the liquid-produced petroleum and accompanying Water invades the zone of in situ combustion the water and the more volatile constituents of the protending to thermally decompose the thus-produced petro' leum leading to the deposition of carbonaceous, preferentially oil-wettable materials or otherwise coat the interstices Yof the formation with preferentially oil-wettable carbonaceous material. This deposition of solid carbonaceous, preferentially oil-wettable material will tend to.

enhance or otherwise improve the oil permeability of the formation surrounding the well bore.

In accordance with one feature of this invention, in order to further enhance the permeability and/ or porosity of the producing formation in the vicinity ofthe well bore after termination of the in situ combustion, there is introduced linto the zone wherein in situ combustion was carried out a relatively cool liquid stream, such as a LPG fraction, a liquid naphtha fraction or a relatively refrac tory gas oil or high boilingV petroleum fractionor crude so as to subject the hot portions Yof the zone swept by in situ combustion to thermal shock, leading to thermal fracturing.

AIn accordance with still another feature of this invention, particularly in the case of a formation wherein prior to treatment by in situ combustion the area immediately surrounding the well 'bore is water blocked, the water block is dissipated from the immediate vicinity of the well bore by injection of a gas such as natural gas, ethane, methane, propane, butane, or a liquid hydrocarbon such as naphtha,v kerosene, gas oil or lube oil fraction, or a hydrocarbon fraction containing finely divided solid combustible material (carbon black) dispersed therein, preferably a hydrocarbon fraction containing dissolved or dispersed therein a surface active agent eifective to reduce the interfacial tension between water and oil, so as to substantially reduce the Water saturation, eg. to a value below about 50% of the pore volume in that portion of the formation immediately surrounding the .well bore. Then there is injected into the formation vvia the well bore the desired combustible material or combustible petroleum fraction to provide the desired fuel for effecting subsequent in situ combustion within that portion of the producing formation.

Any suitable combustible fluid may be employed in the practice of this invention such as a liquid petroleum fraction, e.g. a heavy asphaltic fuel oil or residium orcrude oil previously produced from the formation undergoing treatment. Desirably the injected combustible liquid is an .asphaltic hydrocarbon fraction or one which tends' to deposit a solid carbonaceous material or coke when subjected to thermal cracking or an elevated temperature of about 1000 F., more or less.

As already indicated, the rate and extent of in situ combustion can be altered or controlled by adjusting the oxygen content of the combustible gases being supplied to the in situ combustion zone. Although air is satisfactory, it may be desirable to employ a combustion supporting gas having an oxygen content substantially greater than or substantially less than 20% by Volume, for example, a combustion supporting gas having an oxygen content in the range l-%, such as in the range 1.5- 5% by volume. A suitable combustion supporting gas having the desired oxygen content may be obtained from the exhaust of an internal combustion engine or from hot combustion or ilue gases admixed with varying amounts of air or substantially pure oxygen to obtain the desired oxygen content in the resulting admixture.

In accordance with still another feature of this invention that portion of the formation swept by in situ combustion is suitably treated other than by the deposition of preferentially oil-wettable Ycarbonaceousl material therein to render the formation preferentially oilfwettable.

A vsuitable treatment to render that portion of the forma-v tion preferentially oil-wettable would be to introduce 'into the formation a halosilane such as an aryl, alkaryl or alkyl halosilane, e.g. monomethyl dichloro-monosilane, dimethyl dichloromonosilane, and the like, which readily hydro-A lyzes upon contact with water to form a hydrophobic lm Within the interstices of the formation. f f

The following is explanatory of the practice of this jinvention. Referring now to Fig. 2 of the drawing there is schematically illustrated thereinka brine-free Berea sand? stone core containing a relatively high saturation of a 20 A.P.I. crude. 13% long with a diameter of 1%6". j The core surface was sealed with several brushedcoats of a Plexiglas solution. Sections ofthe core 7zv' long were marked oiiz and, as indicated in Fig. 2, numbered consecutively start-- ing from the end where in situV `combustion was started.v

Sections I-1 yand O-Z were cut from the core for determination of original nitrogen permeability and porosity.

The results are set forth in Table I below.

A 20 A.P.I. crude was obtained from the Hogg Lease, West lColumbia Field, Texas and injected into the core. A gas permeability of 27 md. was established by applying avacuum to section O-1. Sections L2 and O-l were then removed from the core and initial loil saturations of these sections were determined, see Table l.

Thermocouples were wired to the surface ofthe core at the centers of the sections 1-10. A length of stainless steel tubing was placed over the core and the annular space between the tubing and the core was packed with magnesium oxide as an insulator. Air was drawn through the core by placing a vacuum on section 11.

Temperaturedistributions within the core approximating those expected during an in situ combustionY operation` an indication of liquid saturation present in the sectionsA after the simulated in situ combustion. Oil permeabilities were determined using a reiined white oil.` The v.o il.

permeabilities in all sections remained constant after 10 pore volumes of oil were passed through the section being tested and it is these steady-state values which are reported in Table I.

Table I Ng Relative Max. N1 Oil permeoil satn tempermeperme- Core Porosity, ability before perature ability ability section percent before comduring after after combustion, comcomcombnstion percent bustion bustion bustion (md.) F.) (md.)1 (md.)

I1 19. 3 610 I- 19.8 66 i 445 1- l, 000 670 2- 0 536 483 3- 930 568 450 4 880 570 490 780 508 430 690 492 432 520 428 430 350 332 400 9 250 264 340 10 170 165 420 11 49 380 0-1- 19. 9 75 2 466 Ow 19. 6 628 1 Demeasing values indicate increasing liquid saturation.y 2 Cores not subjected to combustion. l Crushed and lost.

The Berea sandstone core used was' If the white oil employed in the permeability test can dissolve out carbonaceous residues not soluble in the inplace crude there would be some question as to the validity of the determination of oil permeability. In order to demonstrate the validity of these tests and to further demonstrate the practicality of this invention as a remedial well treatment operation a rough determination of the coking characteristics of the West Columbia crude employed in the test indicated that 12% by weight of the crude remained as residue after heating in an open vessel at a temperature of 750 F. Core sections I-2 and O-Z whichv were not previously subjected to high temperatures were saturated with a 20 A.P.I. West Columbia crude. Core section I2 was held at 40G-450 F, for 35 minutes and core section O-Z was held at 695-740" F. for minutes. Permeability data obtained on the thus-treated core sections using both West Columbia crude and a refined white oil are listed in Table 1I.

Table II Permeability to Core section Treatment West Columbia crude (md.)

I-2 None.- 490 I-2 400-450 F. (35 min.) 510 O2 None-- 362 0-2 695-740 F. (10 min.) 470 As Table II indicates, there is no reason to believe that the use of a refined white oil rendered the results reported in Table I anomalous.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many changes, substitutions and alterations are possible without departing from the spirit and scope of this invention.

I claim:

l. A process for treating an underground petroleum producing formation penetrated by a well bore which comprises introducing via said well bore into a petroleum producing formation -a liquid petroleum oil which uponl 2. A method of treating a petroleum producing forma-l tion traversed by a well bore which comprises introducing via said Well bore into said petroleum producing formation a combustible liquid which when subjected to thermal cracking tends to deposit a solid carbonaceous material, subsequently introducing via said well bore a combustion supporting gas via said well bore into that portion of said petroleum producing formation containing said liquid, effecting combustion of said liquid within said petroleum producing formation, discontinuing the introduction of said combustion supporting gas into said formation so as to terminate the in situ combustion process therein and subsequently producing petroleum from said formation via said well bore.

3. A method in accordance with claim 2 wherein said combustible liquid comprises a liquid petroleum fraction recovered from said petroleum producing formation.

4. A method in accordance with claim 2 wherein said combustible liquid comprises an asphaltic petroleum oil.

5. A method of treating a petroleum producing formation traversed by a well bore which comprises introducing into said petroleum producing formation via said well bore a combustible liquid which, when subjected to thermal cracking, tends to deposit a solid carbonaceous maten'al such as coke, subsequently introducing via said well bore an oxygen-containing gas into that portion of said petroleum producing formation containing said liquid, effecting in situ combustion of said liquid within said lpetroleum producing formation, terminating the combustion of said liquid within said petroleum producing formation by discontinuing the introduction of said oxygen-containing gas into said petroleum producing formation, introducing a relatively cool hydrocarbon stream via said well bore into that portion of said petroleum producing formation wherein combustion of said liquid was effected and subsequently producing petroleum from said formation via said well bore.

6. A method in accordance with claim 5 wherein said combustible liquid comprises an asphaltic petroleum fraction.

7. A method in accordance with claim 5 wherein said relatively cool hydrocarbon stream comprises a hydrocarbon liquid which when subjected to thermal cracking tends to deposit a solid carbonaceous, preferentially oilwettable material within the interstices of the formation.

References Cited in the file of this patent UNITED STATES PATENTS 1,457,479 Wolcott June 5, 1923 2,642,943 Smith June 23, 1953 2,685,930 Albaugh Aug. 10, 1954 2,761,512 Bond Sept. 4, 1956 2,793,696 Morse May 28, 1957 

1. A PROCESS FOR TREATING AN UNDERGROUNG PETROLEUM PRODUCING FORMATION PENETRATED BY A WELL BORE WHICH COMPRISES INTRODUCING VIA SAID WELL BORE INTO A PETROLEUM PRODUCING FORMATION A LIQUID PETROLEUM OIL WHICH UPON THERMAL CRACKING TENDS TO DEPOSIT A SOLID COMBUSTIBLE CARBONACCEOUS RESIDUE, SUBSEQUENTLY INTRODUCING VIA SAID WELL BORE A COMBUSTION SUPPORTING GAS INTO THAT PORTION OF SAID PETROLEUM PRODUCING FORMATION COTAINING SAID LIQUID PETROLEUM OIL, EFFECTING COMBUSTION OF THE INJECTED LIQUID PETROLEUM OIL THUS INTRODUCED WITHIN SAID PETROLEUM PRODUCING FORMATION, DISCONTINUING THE INTRODUCTION OF SAID COMBUSTION SUPPORTING GAS INTO SAID FORMATION SO AS TO TERMINATE THE IN SITU COMBUSTION PROCESS THEREIN, AND SUBSEQUENTLY PRODUCING PETROLEUM VIA SAID WELL BORE FROM SAID FORMATION THROUGH THE PORTION OF SAID FORMATION WHEREIN SAID INTRODUCED LIQUID PETROLEUM OIL WAS SUBJECTED TO COMBUSTION. 